1. Field of the Invention
[0001] This invention relates to a method and apparatus for minimizing the loss of power
in all or part of a separately excited electromechanical energy conversion system
having, for example, a chopper controller, battery power supply and electromechanical
energy conversion device. An electromechanical energy conversion device having n spatially
fixed windings, n > 1, for producing a magnetic field, and having m movable windings,
m > 1, for producing a magnetic field which opposes the magnetic field produced by
the n spatially fixed windings, is separately excited if the magnetic field produced
by the n spatially fixed windings can be varied, at least in part, independently of
the magnetic field produced by the m movable windings. For example, in a separately
excited dc motor/generator, the n spatially fixed windings can be any combination
of constantly excited field windings, series field windings, and shunt field windings,
with at least one separately excited field winding. The m movable windings can be
armature windings.
[0002] Hereafter, unless otherwise stated, the term "field" will be used to refer to the
electrical circuit of field winding(s). Also, the term "armature" will be used to
refer to the electrical circuit of armature winding(s). This terminology is common
in the literature.
2. Description of the Prior Art
[0003] (a) First, the conversion of electrical energy to mechanical energy in a dc motor
will be considered. Heretofore, the speed and torque control of a separately excited
motor, in the low speed running mode, was carried out by maintaining the field current
constant and varying the armature voltage, and in the high speed running mode, by
maintaining the armature voltage constant and varying the field current. This type
of two speed-range controller was modified by Ohmae et al. (Reference U.S. Patent
number 4,037,144) as follows:
(I) Assume that the field magnetic flux is developed in proportion to the field current
IF.
(II) Assume that the field magnetic flux is independent of the armature current IA.
(III) Assume that the field circuit resistance RF is not a function of field current IF.
(IIIa) For a chopper controller, assume that RF is fixed.
(IV) Assume that the armature circuit resistance RA is not a function of armature current IA.
(IVa) For a chopper controller, assume that RA is fixed.
(V) Then the electrical power loss W=IA2·RA+IF2·RF is minimized when
(VI) Therefore, modify a two speed-range controller to maintain the relationship of
IF to IA as given in (V), unless the value of IF thus calculated exceeds minimum or maximum
limits. In the latter case, maintain IF above the minimum limit or below the maximum limit, respectively.
[0004] The maximum limit on IF is stated by Ohmae et al. to be that level of current which
causes the field magnetic circuit to be saturated. For a range of IF below this limit,
assumptions (I) and (II) are invalid. The reason for this is that the incremental
change in the field magnetic flux caused by a change in the field current is a function
of both the field current magnitude and the armature current magnitude. Assumptions
(III), (IIIa), (IV) and (IVa) can also be significantly inaccurate. The present invention
can achieve higher efficiency because it is not based on the above assumptions.
[0005] The implementation of (VI) by Ohmae et al, still requires a two speed-range controller.
The present invention provides a simpler apparatus.
[0006] In a paper titled "Minimization of Electrical Losses in a Battery Electric Vehicle"
by J. Morton, J. Jones, and C. Watson, presented at Drive Electric 80, Wembley, UK,
October 16, 1980, another scheme for minimizing 1
2R losses in a motor system was presented. In this scheme, field flux is assumed to
be represented by a second degree polynomial in field current, independent of armature
current. Armature chopper duty cycle and field chopper duty cycle are controlled simultaneously
as a function of accelerator pedal position and motor speed. (No algorithm for determining
the appropriate values of armature chopper duty cycle and field chopper duty cycle
for different accelerator pedal positions and motor speeds is given.) Since the armature
chopper duty cycle and the field chopper duty cycle are controlled and not the armature
current and the field current, this method depends on the relationship between chopper
duty cycle and chopper current in order for the system optimization to work. One problem
is that this relationship is dependent on the stability of circuit parameters which
in fact can vary due to manufacturing tolerances, temperature, and component aging.
In particular, the relationship of armature current to armature chopper duty cycle
is very sensitive.
[0007] The present invention makes no assumptions regarding field flux as a function of
field current or armature current. Furthermore, the present invention controls motor
currents directly, which is a more efficacious way to minimize power loss in the system
than controlling chopper duty cycles. Also, the present invention is not limited to
minimizing I
2R losses; all electrical losses can be minimized, such as magnetic losses, which are
modelled as I 2 R losses.
[0008] (b) Second, in considering the conversion of mechanical energy to electrical energy,
no prior references were found regarding power loss minimization.
Objects of the Present Invention
[0009] It is accordingly an object of the present invention to provide a method and apparatus
for minimizing the loss of power in a separately excited electromechanical energy
conversion device and in its controller.
[0010] It is another object of the present invention to provide a method and apparatus for
minimizing total system power loss including power loss in a separately excited electromechanical
energy conversion device, in its controller and in its electrical power source (for
motors) or its electrical load (for generators).
[0011] Another object of the present invention is to provide this minimization both for
the conversion of electrical energy to mechanical energy as well as for the conversion
of mechanical energy to electrical energy.
[0012] Another object of the present invention is to provide this minimization for a wide
variety of motors and generators, including devices having a shunt field as well as
devices lacking a shunt field.
[0013] Viewed from one aspect, there is provided a method for minimizing, by use of a predetermined
optimizing function, the loss of power in a separately excited electromechanical energy
conversion device and in a controller of said energy conversion device, said energy
conversion device having n spatially fixed windings, n > 1, for producing a first
magnetic field, and having m movable windings, m > 1, for producing a second magnetic
field which opposes said first magnetic field produced by said n spatially fixed windings,
such that said first magnetic field produced by said n spatially fixed windings can
be varied, at least in part, independently of said second magnetic field produced
by said m movable windings, said method comprising:
the step of first generating a command signal having a magnitude A;
the step of generating currents I1(A), 12(A),...,In(A) in said n spatially fixed windings, respectively;
and the step of generating currents In+1(A), In+2(A),...,In+m(A) in said m movable windings, respectively;
wherein said currents
are selected in such a manner that their magnitudes as a function of said command
signal having a magnitude A satisfy said predetermined optimizing function;
and wherein said predetermined optimizing function takes into account the incremental
changes in said first and second magnetic fields caused by each of said n+m currents
in each of said n+m windings.
[0014] Viewed from another aspect there is provided an apparatus for minimizing, by use
of a predetermined optimizing function, the loss of power in a separately excited
electromechanical energy conversion device and in a controller of said energy conversion
device, said energy conversion device having n spatially fixed windings, n > 1, for
producing a first magnetic field, and having m movable windings, m > 1, for producing
a second magnetic field which opposes said first magnetic field produced by said n
spatially fixed windings, such that said first magnetic field produced by said n spatially
fixed windings can be varied, at least in part, independently of said second magnetic
field produced by said m movable windings, said apparatus comprising:
means for first generating a command signal having a magnitude A;
means for generating currents II(A), I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A), In+2(A),...,In+m(A) in said m movable windings, respectively;
wherein said currents
are selected in such a manner that their magnitudes as a function of said command
signal having a magnitude A satisfy said predetermined optimizing function;
and wherein said predetermined optimizing function takes into account the incremental
changes in said first and second magnetic fields caused by each of said n+m currents
in each of said n+m windings.
[0015] Certain embodiments of the invention will now be described by way of example.
Brief Description of the Drawings
[0016]
Fig. 1 is a block diagram of a separately excited electromechanical energy conversion
device with a "Long shunt" field;
Fig. 2 is a block diagram of a separately excited electromechanical energy conversion
device with a "Short shunt" field;
Fig. 3 is a block diagram of one embodiment of the present invention;
Fig. 4 is a block diagram of another embodiment of the present invention;
Fig. 5 is a block diagram of another embodiment of the present invention;
Fig. 6 is a block diagram of another embodiment of the present invention;
Fig. 7 is a block diagram of another embodiment of the present invention;
Fig. 8 is a block diagram of another embodiment of the present invention;
Fig. 9 is a schematic of an External Command Device;
Fig. 10 is a schematic of a Function Generator;
Fig. 11 is a schematic of an Armature Controlling Circuit;
Fig. 12 is a schematic of a Field Controlling Circuit;
Fig. 13 is a schematic of an Armature Driving Circuit;
Fig. 14 is a schematic of a Field Driving Circuit;
Fig. 15 is a schematic of a forward or step down chopper control circuit; and
Fig. 16 is a schematic of a flyback or step up chopper control circuit.
The Method
[0017] The following derivation is applicable to an energy conversion device, in particular
to a dc motor/generator with an armature, a permanent magnet field, a constantly excited
field, a series field, a long shunt field or a short shunt field, and a separately
excited field. An optimizing function f
OPT is derived, wherein f
OPT gives the desired relationship between the currents in the various windings of the
device in order for the total power loss in the system to be minimized. For other
types or other configurations of energy conversion devices, a similar derivation will
produce the corresponding optimizing function f
OPT. The optimizing function f
OPT can be predetermined from the characteristics of the energy conversion system being
optimized; or f
OPT can be periodically determined by an adaptive controller that measures, directly
or indirectly, any characteristics of the energy conversion system that can vary.
[0018] In applying this method, approximations of f
OPT can be used, with the resulting power losses dependent upon the accuracy of the approximation.
Examples of approximations of f
OPT that can be used are: a power series approximation; a piecewise-linear approximation;
and a sum of step functions approximation.
[0019] Furthermore, the currents in the various windings of the energy conversion device
can each be a different function of the command signal that operates the controller,
as long as these currents satisfy the optimizing function f
OPT. That is, if the amplitude of the command signal is A, and if the current in winding
i of the energy conversion device is I
i (A), where I > i > n+m, then overall power losses are minimized if I
1(A). I
2(A),...,I
n(A),I
n+1(A), I
n+2(A),...,I
n+m(A) satisfy the optimizing function f
OPT.
[0020] Because the method of the present invention can be practiced in different ways, the
drawings relating to the description of this method show only the driving circuits
of the controller connected to the energy conversion device. Fig. 1 illustrates a
controller connected to a device with a Long Shunt Field 1. FIG. 2 illustrates a controller
connected to a device with a Short Shunt Field 2. For the energy conversion device
and the controller,
where I = Shunt Field current
IA = Armature current
IF = Separately Excited Field current
IC = Constantly Excited Field current
RP = resistance of Shunt Field (1 in FIG. 1, 2 in FIG. 2)
RF = sum of resistance of Separately Excited Field (3 in FIGS. 1 and 2) and Separately
Excited Field Driving Circuit (4 in FIGS.1 and 2)
RC = sum of resistance of Constantly Excited Field (5 in FIGS. 1 and 2) and Constantly
Excited Field Driving Circuit (6 in FIGS.1 and 2)
[0021] R
A1 and R
A2 are defined differently for the Long Shunt configuration and the Short Shunt configuration:
RAl = sum of resistance of Series Field 8 and Armature 9 (FIG. 1); or
RAl = resistance of Armature 9 (FIG. 2)
RA2 = resistance of Armature Driving Circuit 10 (FIG. 1); or
RA2 = sum of resistance of Series Field 8 and Armature Driving Circuit 10 (FIG. 2)
[0022] By using these two definitions for R
A1 and R
A2' the following discussion applies to both the Long Shunt configuration (FIG. 1) and
the Short Shunt configuration (FIG. 2), although the remaining drawings illustrate
only the Long Shunt configuration.
where T = mechanical torque input or output
Ø = strength of Permanent Magnet Field (7 in FIGS.1 and 2)
Substituting IA =
into (1):
[0023] Differentiating (2) with respect to IF and setting the result equal to zero:
Substituting I
A for
in (3);
f
E(I
P,I
A,I
F,I
C,Ø) can be measured, for example, by performing a blocked rotor test on the energy
conversion device. With I
C and Ø constant, T can be measured for different values of Ip, I
A, and IF. Then
[0024] Therefore, (4) can be solved numerically to give
f
OPT is the optimizing function referred to previously. If the energy conversion device
lacks a shunt field, then (4) becomes
where
[0025] (
5) can be solved numerically for I
F = f
OPT(I
A) or I
A = f
OPT-1(I
F).
[0026] If R
A and R have only small nonlinearities, then
and
are small and (5) becomes
[0027] When an armature or a field driving circuit is, in particular, a chopper, the value
of that circuit's resistance becomes dependent on the chopper duty cycle. This is
because the power source resistance (for motors) or the load resistance (for generators)
is switched in and out by the chopper. In a system having an electromechanical energy
conversion device with n + m windings, the duty cycle of the chopper circuit that
drives winding i is D
i, ≤ i < n + m. The following is a detailed analysis of this effect.
[0028] The schematic of a forward or step down chopper circuit is shown in FIG. 15. The
load 61 can be a motor armature winding (E = back emf, E < V) or a motor field winding
(E=O). When the electronic switch
62 is closed, current I
SOURCE flows from the voltage source whose voltage is V. Current I
MOTOR flows through the load 61, the inductor 63, and the switch 62. When the switch 62
is open, I
MOTOR flows through the load 61, the inductor 63, and the freewheeling diode 64. With no
filter 65, I
SOURCE =
IMOTOR when the switch 62 is closed, and I
SOURCE = 0 when the switch 62 is open. Let
RMOTOR = the resistance of the motor/generator 61
RSWITCH = the resistance of the electronic switch 62
RINDUCTOR = the resistance of the inductor 63
RDIODE the resistance of the freewheeling diode 64
[0029] R
SOURCE = the resistance of the voltage source D. = the fraction of the time that the switch
62 is on, i.e., the duty cycle of the chopper. As previously indicated, generally
D
i is the duty cycle for an armature chopper or a field chopper.
[0030] Then the effective resistance to current I
MOTOR is
[0031] If the current flowing into the voltage source whose voltage is V is filtered by
filter 65 so that I
SOURCE is nearly constant, then
[0032] The equivalent source resistance to I
MOTOR is
x R
SOURCE. Then
[0033] The schematic of a flyback or step up chopper circuit is shown in Figure 16. This
circuit applies only to a motor armature winding, with E < V. When the electronic
switch 62 is closed, current I
MOTOR flows through the armature winding 61, the inductor 63, and the switch 62. When the
switch 62 is open,
IMOTOR flows in the armature winding 61, the inductor 63, and the freewheeling diode 64.
With no filter 65, I
SOURCE =
IMOTOR when the switch
62 is open, and I
SOURCE = 0 when the switch 62 is closed.
[0034] The effective resistance to current I
MOTOR is
[0035] If the current flowing into the voltage source whose voltage is V is filtered by
filter 65 so that I
SOURCE is nearly constant, then I
SOURCE = (1 -
Di) x I
MOTOR. The equivalent source resistance to I
MOTOR is (1 - D
i)
2 x R
SOURCE. Then
[0036] For an armature circuit, this dependence of circuit resistance on chopper duty cycle
can be converted to an equivalent dependence of circuit resistance on motor speed.
The following is a detailed analysis of this effect.
[0037] For a forward converter driving an armature winding
[0038] where R
A is the armature circuit resistance and ω is the motor speed in radians per second.
[0039] For a step up converter
[0040] In both cases, D
i is related to ω. Hereafter [D
1, D
2, ..., D
n+m] is referred to simply as D a multi-valued variable; also,.in defining D, ω can be
substituted for any D. that is the duty cycle of a chopper driving an armature winding.
In this way, the dependence of f
OPT on D is made more general.
[0041] In energy conversion systems having a high power source resistance (for motors) or
a high load resistance (for generators), as for example in battery powered systems,
this effect is important. In such cases the function f
OPT becomes dependent on the duty cycles
D of the various chopper driving circuits. In practical systems, the variation of armature
circuit resistance will have the predominant effect on f
OPT. Therefore, in such systems, dependence of f
OPT on D is reduced to a dependence on the armature chopper duty cycle, or equivalently,
on W.
[0042] Another result of specifically using a chopper for a driving circuit is the presence
of an ac ripple in that circuit's output current. This ac component can cause an effective
change in the resistance of the motor or generator winding that it passes through.
This is due to form factor 12R losses, skin effect, and magnetic losses, such as eddy
currents and hysteresis. All of these physical effects can be modeled by making the
effective circuit resistance a function of both dc current and ac current. Since ac
current is a function of chopper duty cycle D
i, f
OPT is dependent on D. Thus, different loss mechanisms are modeled as 12R losses, which
then allows the optimization scheme of the present invention to be applied. Since
accurate modeling of motor systems using chopper controllers is difficult, the determination
of equivalent resistances may have to be done entirely experimentally.
[0043] Reference: "Series Motor Parameter Variations as a Function of Frequency and Saturation",
by H.B. Hamilton and Elias Strangas, IEEE PES Winter Meeting, New York, NY, February
3-8, 1980.
[0044] In fact, f
OPT can be determined entirely experimentally. A motor or generator is operated at a
fixed torque and speed while the separately excited field current is varied. The value
of separately excited field current that minimizes the input power to the system (for
a motor) or that maximizes the output power (for a generator) is the desired value
at that torque and speed. Those values, along with the corresponding values of armature
current for each torque and speed, are the values of f
OPT.
[0045] Accordingly, the power loss minimization of the present invention is achieved for
separately excited electromechanical energy conversion devices having a shunt field
by controlling the separately excited field current, I
F, so as to be f
OPT (I
A'I
P), where IF
= f
OPT[I
A,I
P) is the solution to (4).
[0046] Accordingly, also, the power loss minimization of the present invention is achieved
for separately excited electromechanical energy conversion devices lacking a shunt
field by simultaneously controlling the armature current, I
A, and the separately excited field current; T
F, such that IF = f
OPT(I
A) or I
A = f
OPT-1(I
F), where the latter is the solution to 5.
The Apparatus
[0047] 1. Two embodiments of the present invention for separately excited electromechanical
energy conversion devices having a shunt field are described.
[0048] (a) FIG. 3 is a block diagram of one embodiment of the present invention. The External
Command Device 11 generates a current command V
IAPC to the Armature Controlling Circuit 12. This in turn operates the Armature Driving
Circuit 10, causing the Armature 9 and the Series Field 8, in parallel with the Shunt
Field 1, to have a total current equal to I
A+I
P flowing in them. Shunt Field current Ip is detected by the Shunt Field Current Sensor
13 which outputs signal V
IPD to the Function Generator 14. The latter, which also receives V
IAPC from the External Command Device, generates a current command V
IFC to the Field Controlling Circuit 15, where VIFC = f
OPT [(V
IAPC - V
IPD), V
IPD]. This in turn operates the Field Driving Circuit 4, driving current IF through the
Separately Excited Field 3, where IF
= f
OPT(I
A, I
P).
[0049] If the embodiment of FIG. 3 were a chopper controller, then function generator 14
would also receive a signal representing the duty cycle D, as shown in dotted lines.
The effect of this would be to minimize total system power loss.
[0050] (b) FIG. 4 is a block diagram of another embodiment of the present invention. The
External Command Device 11 generates a command V
AC to the Armature Controlling Circuit 12. This in turn operates the Armature Driving
Circuit 10. Armature current I
A is detected by the Armature Current Sensor 16, which outputs signal V
IAD to the Function Generator 14. Shunt Field current I
P is detected by the Shunt Field Current Sensor 13, which outputs signal V
IPD to the Function Generator. The latter generates a current command V
IFC to the Field Controlling Circuit 15, where V
IFC = f
OPT(V
IAD, V
IPD). This in turn operates the Field Driving Circuit 4, driving current IF through the
Separately Excited Field
3, where IF
= fO
PT(
IA,Ip).
[0051] If there is no permanent magnet field and no constantly excited field in the energy
conversion device, and if this embodiment is used for converting mechanical energy
to electrical energy, then f
OPT may have to be changed slightly to make I
F non-zero when I
A is zero. Otherwise, generation may not be able to start up.
[0052] If the embodiment of FIG. 4 were a chopper controller, then function generator 14
would also receive a signal representing the duty cycle D for reasons described in
connection with FIG.3,
[0053] 2. Four embodiments of the present invention for separately excited electromechanical
energy conversion devices lacking a shunt field are described. Before discussing these
four embodiments, note that FIGS. 5-8 show the signal representing the duty cycle
D should these embodiments be chopper controllers and for reasons previously described.
[0054] (a) FIG. 5 is a block diagram of another embodiment of the present invention. The
External Command Device 11 generates a current command V
IAC to the Armature Controlling Circuit 12. This in turn operates the Armature Driving
Circuit 10, causing the Armature 9 and the Series Field 8 to have current I
A flowing in them. V
IAC also operates the Function Generator 14, which generates current command V
IFC to the Field Controlling Circuit 15, where VIFC = f
OPT(V
IAC). This in turn operates the Field Driving Circuit 4, driving current IF through the
Separately Excited Field 3, where IF
= f
OPT(I
A).
[0055] (b) FIG. 6 is a block diagram of another embodiment of the present invention. The
External Command Device 11 generates a command V
AC to the Armature Controlling Circuit 12. This in turn operates the Armature Driving
Circuit, 10. Armature current I
A is detected by the Armature Current Sensor 16, which outputs signal V
IAD to the Function Generator 14. The latter generates a current command V
IFC to the Field Controlling Circuit 1
5, where
VIFC = f
OPT(V
IAD). This in turn operates the Field Driving Circuit 4, driving current IF through the
Separately Excited Field 3, where IF =f
OPT(I
A).
[0056] If there is no permanent magnet field and no constantly excited field in the energy
conversion device, and if this embodiment is used for converting mechanical energy
to electrical energy, then f
OPT may have to be changed slightly to make IF non-zero when I
A is zero. Otherwise, generation may not be able to start up.
[0057] (c) FIG. 7 is a block diagram of another embodiment of the present invention. The
External Command Device 11 generates a current command V
IFC to the Field Controlling Circuit 15. This in turn operates the Field Driving Circuit
4, driving current IF through the Separately Excited Field 3. V
IFC also operates the Function Generator 14, which generates a current command V
IAC to the Armature Controlling Circuit 12, where V
IAC = f
OPT-1(V
IFC). This in turn operates the Armature Driving Circuit 10, causing the Armature 9 and
the Series Field 8 to have current I
A flowing in them, where I
A = f
OPT-1(I
F).
[0058] (d) FIG. 8 is a block diagram of another embodiment of the present invention. The
External Command Device 11 generates a command V
FC to the Field Controlling Circuit 15. This in turn operates the Field Driving Circuit
4. Separately Excited Field current IF is detected by the Separately Excited Field
Current Sensor 17, which outputs signal V
IFD to the Function Generator 14. The latter generates a current command V
IAC to the Armature Controlling Circuit 12, where
VIAC = f
OPT-1(V
IFD). This in turn operates the Armature Driving Circuit 10, causing the Armature 9 and
the Series Field 8 to have current I
A flowing in them, where I
A = fOPT
-1(I
F).
[0059] 3. These embodiments of the present invention are constructed with functional blocks
whose implementation is known to those skilled in the art. However, for completeness,
a brief description of some of the ways in which each functional block can be implemented
is included. The numbers refer to FIGS. 3 through 8.
(a) The External Command Device 11 can be a voltage source, such as a variable resistor
with one end grounded, the other end connected to a fixed voltage, and the center
tap as the output.
(b) The Armature Controlling Circuit 12 and the Field Controlling Circuit 15 can each
be implemented as a time ratio control circuit. This can be a pulse width modulator
operating at a fixed frequency. It can also be a voltage to frequency converter operating
with a fixed pulse width. Variable pulse width and variable frequency operation can
be combined together to achieve time ratio control, also.
(c) The Armature Driving Circuit 10 and the Field Driving Circuit 4 can each be implemented
by various power switching devices combined with a diode. Driven by a time ratio control
circuit, the switching device is operated to be alternately on (conducting) or off
(non-conducting). The diode allows current to flow in the load during the time that
the switching device is off. Silicon-controlled rectifiers, power transistors, Darlington
transistors, and power field effect transistors are all commonly employed in this
application. For high current controllers, a parallel connection of these parts can
be used to achieve the desired current handling capability.
(d) The Armature Current Sensor 16, the Shunt Field Current Sensor 13, and the Separately
Excited Field Current Sensor 17 can each be implemented by a non-inductive resistor,
such as those used as ampere meter shunts. Another type of device that can be used
is a Hall effect current probe.
(e) The Function Generator 14 can be implemented by using one of several analog techniques.
A power series approximation of fOPT or fOPT-1 can be constructed with multipliers and summing amplifiers. A piecewise-linear approximation
of fOPT or fOPT-1 can be built using amplifiers and diodes. An excellent reference on this topic is
the "Nonlinear Circuits Handbook" published by Analog Devices, Inc., Norwood, Massachusetts
02062, 1974, chapter 2-1.
[0060] A combination digital and analog technique can also be used. A Read Only Memory (ROM)
serves as a look up table for the desired function. The ROM is addressed by the digital
output of an analog to digital converter (for f
OPT(I
A) or f
OpT-1(I
F)) or converters (for f
OPT(I
A,I
P)). The output of the ROM feeds a digital to analog converter to change the digital
value of the function to analog form.
[0061] In the case of f
OPT being dependent on D an analog signal proportional to D. can be obtained by low pass
filtering the pulse train that drives the switch in chopper i. The previously described
analog or combination analog-digital techniques can then be applied.
[0062] 4. FIGS. 9 through 14 are the schematic of a controller designed for use in an electric
vehicle. This controller can drive a dc motor or it can operate the motor as a generator
to recharge the vehicle's batteries (regenerative braking). Each figure of the schematic
shows one functional block of FIG. 5, upon which this controller is based.
(a) FIG. 9 is the schematic of an External Command Device. The armature current command
VIAC is selected by the multiplexer 18 from the analog output of either the 5 kilohm potentiometer
in the accelerator pedal 19 or the 5 kilohm potentiometer in the brake pedal 20. The
selection of the command source is made by the digital signal BRAKEB, which comes
from a switch in the brake pedal 21. The signal SHUTDOWN turns off the controller
when neither pedal is engaged or when both pedals are engaged.
(b) FIG. 10 is the schematic of a Function Generator. Armature current command VIAC is compared to two reference voltages by comparators 24 and 25. The digital outputs
of the comparators control the multiplexer 26, which selects a fixed offset (through
the X inputs of the multiplexer) to be added to a selected fraction of VIAC (through the Y inputs of the multiplexer). The result is the field current command
VIFC. The values of the resistors are chosen to make VIFC≈fOPT(VIAC) for the particular motor being used. fOPT(VIAC) is approximated by a four section piecewise-linear function of VIAC. The first three
sections are achieved by selecting resistor values to make the fractions of VIAC going into the Y inputs of the multiplexer equal to the slopes of the piecewise-linear
approximation above each of the first three breakpoints, and by selecting the values
of the remaining resistors to make the fixed offsets going into the X inputs of the
multiplexer such that VIFC = fOPT(VIAC) at the first three breakpoints of the piecewise-linear approximation. The fourth
section is a current limit region, and is reached when the +Current Limit Sense input
of the Field Controlling Circuit pulse width modulator (37 in FIG. 12) receives a
signal greater than +200 millivolts.
(c) FIG. 11 is the schematic of an Armature Controlling Circuit. The output of the
current sensor 27 is amplified times 32 by a differential amplifier circuit whose
active elements are amplifiers 28 and 29. The multiplexer 61 selects between an inverting
differential amplifier circuit and a non-inverting differential amplifier circuit.
This is necessary because current in the current sensor flows in one direction during
accelerating and in the other direction during braking. The pulse width modulator
30 receives its current command VIAC from the External Command Device (FIG. 9) and receives a reference related to the
amount of current flowing in the armature from the output of the differential amplifier
circuit. The output of the pulse width modulator is low true ANDed separately with
ACCELERATES and BRAKEB by OR gates 31 and 32. The resulting signals and their complements,
namely PWMACCELB and PWMACCEL, and PWMBRAKEB and PWMBRAKE, operate the Armature Driving
Circuit. SYNCB and C connect to the Field Controlling Circuit (FIG. 12) and synchronize
the pulse width modulator in that circuit with the Armature Controlling Circuit pulse
width modulator.
(d) FIG. 12 is the schematic of a Field Controlling Circuit. The output of the current
sensor 35 is amplified times 32 by a differential amplifier circuit whose active element
is amplifier 36. The amplifier's output provides the pulse width modulator 37 with
a reference related to the amount of current flowing in the field winding. The pulse
width modulator receives its current command VIFC from the Function Generator (FIG. 10). SYNCB and C originate in the Armature Controlling
Circuit (FIG. ll) and synchronize the pulse width modulators 30 and 37 in the two
controlling circuits. The output of the pulse width modulator 37 is PWMFIELDB. This
signal and its complement, PWMFIELD, operate the field driving circuit.
(e) FIG. 13 is the schematic of an Armature Driving Circuit. In the accelerating mode,
when PWMACCEL goes high transistor 39 turns on, which then turns on the high current
transistor 40. When PWMACCEL is low, there is no base drive to transistor 40 from
transistor 39. Also, PWMACCELB is high, turning on transistor 41, which then turns
on transistor 42. The latter removes stored charge from high current transistor 40,
causing it to turn off rapidly. When high current transistor 40 is off, current flowing
in the armature can continue to circulate through diode 43. The result is a dc-dc
converter from V+ to the motor back emf, where V+> back emf.
[0063] In the regenerative braking mode, when PWMBRAKEB goes low transistor 44 turns on,
which then turns on the high current transistor 45. When PWMBRAKEB is high, there
is no base drive to transistor 45 from transistor 44. Also, PWMBRAKE is low, turning
on transistor 46, which then turns on transistor 47. The latter removes stored charge
from high current transistor 45, causing it to turn off rapidly. When high current
transistor 45 is off, current flowing in the armature can flow through diode 48 into
the V+ supply. The result is a dc-dc converter from the motor back emf to V+, where
V+> back emf.
[0064] This circuit is rated for 20 Amperes of armature current. For each additional 20
Amperes of current, the circuitry within the dotted line 49 must be replicated and
added in parallel to that shown in FIG. 13. If this is done, then the values of the
base resistors 50 and 51 for high current transistors 40 and 45, respectively, must
be selected individually for each of the paralleled transistors such that they share
their load equally.
[0065] (f) FIG. 14 is the schematic of a Field Driving Circuit. Its operation is identical
to that of the Armature Driving Circuit in the accelerating mode.
[0066] (g) The following table gives the manufacturer and the manufacturer's part number
for the integrated circuits and transistors in this controller. Two gates from the
same integrated circuit together in parallel for greater drive capability is indicated
by
*.
[0067] The above description of embodiments of the present invention provides a general
method for improving the operating efficiency of electromechanical energy conversion
devices and also provides several embodiments of the invention. Controllers embodying
the present invention can be used, for example, in industrial motor control, electric
vehicle control (including both accelerating and regenerative braking) and the control
of generators. Additional possible variations of the method and apparatus of the present
invention will be evident to those skilled in the art.
1. A method for minimizing, by use of a predetermined optimizing function, the loss
of power in a separately excited electromechanical energy conversion device and in
a controller of said energy conversion device, said energy conversion device having
n spatially fixed windings, n > 1, for producing a first magnetic field, and having
m movable windings, m > 1, for producing a second magnetic field which opposes said
first magnetic field produced by said n spatially fixed windings, such that said first
magnetic field produced by said n spatially fixed windings can be varied, at least
in part, independently of said second magnetic field produced by said m movable windings,
said method comprising:
the step of first generating a command signal having a magnitude A;
the step of generating currents I1(A), 12(A),...,In(A) in said n spatially fixed windings, respectively;
and the step of generating currents In+1(A), In+2(A),...,In+m(A) in said m movable windings, respectively;
wherein said currents
are selected in such a manner that their magnitudes as a function of said command
signal having a magnitude A satisfy said predetermined optimizing function;
and wherein said predetermined optimizing function takes into account the incremental
changes in said first and second magnetic fields caused by each of said n+m currents
in each of said n+m windings.
2. An apparatus for minimizing, by use of a predetermined optimizing function, the
loss of power in a separately excited electromechanical energy conversion device and
in a controller of said energy conversion device, said energy conversion device having
n spatially fixed windings, n > 1, for producing a first magnetic field, and having
m movable windings, m > 1, for producing a second magnetic field which opposes said
first magnetic field produced by said n spatially fixed windings, such that said first
magnetic field produced by said n spatially fixed windings can be varied, at least
in part, independently of said second magnetic field produced by said m movable windings,
said apparatus comprising:
means for first generating a command signal having a magnitude A;
means for generating currents I1(A), 12(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A), In+2(A),...,In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A). In+2(A),...,In+m(A) are selected in such a manner that their magnitudes as a function of said command
signal having a magnitude A satisfy said predetermined optimizing function;
and wherein said predetermined optimizing function takes into account the incremental
changes in said first and second magnetic fields caused by each of said n+m currents
in each of said n+m windings.
3. An apparatus as in claim 2 wherein the n spatially fixed windings comprise at least
a shunt field winding and a separately excited field winding, and wherein the m movable
windings comprise armature windings; and
wherein said means for generating currents Il(A),I2(A), ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving said command signal
A and receiving a signal representing the magnitude of current in said shunt field
winding.
4. An apparatus as in claim 2 wherein the n spatially fixed windings comprise at least
a shunt field winding and a separately excited field winding, and wherein the m movable
windings comprise armature windings; and
wherein said means for generating currents I1(A),I2(A) , ...,I (A) includes function generator means for generating said currents in
the separately excited field winding, said function generator means receiving a signal
representing the magnitude of current in said armature windings and receiving a signal
representing the magnitude of current in said shunt field winding.
5. An apparatus as in claim 2 wherein the n spatially fixed windings comprise at least
a separately excited field winding, and wherein the m movable windings comprise armature
windings; and
wherein said means for generating currents I1(A),I2(A), ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving said command signal
A.
6. An apparatus as in claim 2 wherein the n spatially fixed windings comprise at least
a separately excited field winding, and wherein the m movable windings comprise armature
windings; and
wherein said means for generating currents I1(A),I2(A), ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving a signal representing
the magnitude of current in said armature windings.
7. An apparatus as in claim 2 wherein the n spatially fixed windings comprise at least
a separately excited field winding, and wherein the m movable windings comprise armature
windings; and
wherein said means for generating currents In+1(A), In+2(A),...,In+m(A) includes function generator means for generating said currents in the armature
windings, said function generator means receiving said command signal A.
8. An apparatus as in claim 2 wherein the n spatially fixed windings comprise at least
a separately excited field winding, and wherein the m movable windings comprise armature
windings; and
wherein said means for generating currents In+1(A), In+2(A),...,In+m(A) includes function generator means for generating said currents in the armature
windings, said function generator means receiving a signal representing the magnitude
of current in said separately excited field winding.
9. A method for minimizing, by use of an optimizing function, the total loss of power
in a circuit having power loss components including a separately excited electromechanical
energy conversion device, a controller of said energy conversion device, and a power
source if said energy conversion device is a motor or a load if said energy conversion
device is a generator, said energy conversion device having n spatially fixed windings.,
n > 1, for providing a first magnetic field, and having m movable windings, m > 1,
for producing a second magnetic field which opposes said first magnetic field produced
by said n spatially fixed windings, such that said first magnetic field produced by
said n spatially fixed windings can be varied, at least in part, independently of
said second magnetic field produced by said m movable windings, said method comprising;
the step of first generating a command signal A;
the step of generating currents Il(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and the step of generating currents In+l(A),In+2(A),..., In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A), In+2(A),...,In+m(A) are selected in such a manner that their magnitudes as a function of said command
signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said first and second magnetic fields caused by each of said n+m currents in each
of said n+m windings.
10. An apparatus for minimizing, by use of an optimizing function, the total loss
of power in a circuit having power loss components including a separately excited
electromechanical energy conversion device, a controller of said energy conversion
device, and a power source if said energy conversion device is a motor or a load if
said energy conversion device is a generator, said energy conversion device having
n spatially fixed windings, n > 1, for providing a first magnetic field, and having
m movable windings, m > 1, for producing a second magnetic field which opposes said
first magnetic field produced by said n spatially fixed windings, such that said first
magnetic field produced by said n spatially fixed windings can be varied, at least
in part, independently of said second magnetic field produced by said m movable windings,
said apparatus comprising:
means for first generating a command signal A;
means for generating currents I1(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A),In+2(A),..., In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),....In(A),In+1(A), In+2(A),...,In+m(A) are selected in such a manner that their magnitudes as a
function of said command signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said first magnetic field caused by said n currents in each of said n windings.
11. An apparatus for minimizing, by use of an optimizing function, the total loss
of power in a circuit having power loss components including a separately excited
electromechanical energy conversion device, a controller of said energy conversion
device, and a power source if said energy conversion device is a motor or a load if
said energy conversion device is a generator, said energy conversion device having
n spatially fixed windings, n > 1, for providing a first magnetic field, and having
m movable windings, m > 1, for producing a second magnetic field which opposes said
first magnetic field produced by said n spatially fixed windings, such that said first
magnetic field produced by said n spatially fixed windings can be varied, at least
in part, independently of said second magnetic field produced by said m movable windings,
said apparatus comprising:
means for first generating a command signal A;
means for generating currents Il(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A),In+2(A), ...,In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A), In+2(A),...,In+m(A), are selected in such a manner that their magnitudes as a function of said command
signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said first magnetic field caused by said m currents in each of said m windings.
12. An apparatus for minimizing, by use of an optimizing function, the total loss
of power in a circuit having power loss components including a separately excited
electromechanical energy conversion device, a controller of said energy conversion
device, and a power source if said energy conversion device is a motor or a load if
said energy conversion device is a generator, said energy conversion device having
n spatially fixed windings having resistance, n > 1, for providing a first magnetic
field, and having m movable windings, m > 1, for producing a second magnetic field
which opposes said first magnetic field produced by said n spatially fixed windings,
such that said first magnetic field produced by said n spatially fixed windings can
be varied, at least in part, independently of said second magnetic field produced
by said m movable windings, said apparatus comprising:
means for first generating a command signal A;
means for generating currents Il(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A),In+2(A), ...,In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A), In+2(A),...,In+m(A) are selected in such a manner that their magnitudes as a function of said command
signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said resistance of said n windings as a function of said n currents.
13. An apparatus for minimizing, by use of an optimizing function, the total loss
of power in a circuit having power loss components including a separately excited
electromechanical energy conversion device, a controller of said energy conversion
device, and a power source if said energy conversion device is a motor or a load if
said energy conversion device is a generator, said energy conversion device having
n spatially fixed windings, n > 1, for providing a first magnetic field, and having
m movable windings having resistance, m > 1, for producing a second magnetic field
which opposes said first magnetic field produced by said n spatially fixed windings,
such that said first magnetic field produced by said n spatially fixed windings can
be varied, at least in part, independently of said second magnetic field produced
by said m movable windings, said apparatus comprising:
means for first generating a command signal A;
means for generating currents Il(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A),In+2(A), ...,In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A). In+2(A),...,In+m(A) are selected in such a manner that their magnitudes as a function of said command
signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said resistance of said m windings as a function of said m currents.
14. An apparatus for minimizing, by use of an optimizing function, the total loss
of power in a circuit having power loss components including a separately excited
electromechanical energy conversion device, a controller of said energy conversion
device, and a power source if said energy conversion device is a motor or a load if
said energy conversion device is a generator, said energy conversion device having
n spatially fixed windings having resistance, n > 1, for providing a first magnetic
field, and having m movable windings having resistance, m > 1, for producing a second
magnetic field which opposes said first magnetic field produced by said n spatially
fixed windings, such that said first magnetic field produced by said n spatially fixed
windings can be varied, at least in part, independently of said second magnetic field
produced by said m movable windings, said apparatus comprising:
means for first generating a command signal A;
means for generating currents I1(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A),In+2(A), ...,In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A). In+2(A),...,In+m(A)are selected in such a manner that their magnitudes as a function of said command
signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said resistance of said n+m windings as a function of said n+m currents.
15. An apparatus for minimizing, by use of a predetermined optimizing function, the
total loss of power in a circuit having power loss components including a separately
excited electromechanical energy conversion device, a controller of said energy conversion
device, and a power source if said energy conversion device is a motor or a load if
said energy conversion device is a generator, said energy conversion device having
n spatially fixed windings, n > 1, for providing a first magnetic field, and having
m movable windings, m > 1, for producing a second magnetic field which opposes said
first magnetic field produced by said n spatially fixed windings, such that said first
magnetic field produced by said n spatially fixed windings can be varied, at least
in part, independently of said second magnetic field produced by said m movable windings,
said apparatus comprising:
means for first generating a command signal A;
means for generating currents I1(A),I2(A),...,In(A) in said n spatially fixed windings, respectively;
and means for generating currents In+1(A),In+2(A), ...,In+m(A) in said m movable windings, respectively;
wherein said currents I1(A),I2(A),...,In(A),In+1(A), In+2(A),...,In+m(A) are selected in such a manner that their magnitudes as a function of said command
signal A satisfy said optimizing function;
and wherein said optimizing function takes into account the incremental changes in
said first and second magnetic fields caused by each of said n+m currents in each
of said n+m windings.
16. An apparatus as in claim 15 wherein the n spatially fixed windings comprise at
least a shunt field winding and a separately excited field winding, and wherein the
m movable windings comprise armature windings and wherein said controller is a chopper
controller having a multi-valued duty cycle D, where D =[Di for said chopper controller that produces Ii (A) , 1 < i < n+m]; and
wherein said means for generating currents I1(A),I2(A), ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving said command signal
A, a signal representing the magnitude of current in said shunt field winding and
a signal representing the duty cycle D.
17. An apparatus as in claim 15 wherein the n spatially fixed windings comprise at
least a shunt field winding and a separately excited field winding, and wherein the
m movable windings comprise armature windings and wherein said controller is a chopper
controller having a multi-valued duty cycle D, where D =[Di for said chopper controller that produces current Ii(A) , 1 < i < n+m]; and
wherein said means for generating currents I1(A),I2(A), ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving a signal representing
the magnitude of current in said armature windings, a signal representing the magnitude
of current in said shunt field winding and a signal representing the duty cycle D.
18. An apparatus as in claim 15 wherein the n spatially fixed windings comprise at
least a separately excited field winding, and wherein the m movable windings comprise
armature windings and wherein said controller is a chopper controller having a multi-valued
duty cycle D, where D = D1 for said chopper controller that produces current Ii (A) , 1 < i < n+m]; and
wherein said means for generating currents I1(A) ,I2(A) , ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving said command signal
A and a signal representing the duty cycle D.
19. An apparatus as in claim 15 wherein the n spatially fixed windings comprise at
least a separately excited field winding, wherein the m movable windings comprise
armature windings and wherein said controller is a chopper controller having a multi-valued
duty cycle D, where D =[Di for said chopper controller that produces current Ii (A) , 1 < i < n+m]; and
wherein said means for generating currents Il(A),I2(A), ...,In(A) includes function generator means for generating said currents in the separately
excited field winding, said function generator means receiving a signal representing
the magnitude of current in said armature windings and a signal representing the duty
cycle D.
20. An apparatus as in claim 15 wherein the n spatially fixed windings comprise at
least a separately excited field winding, and wherein the m movable windings comprise
armature windings and wherein said controller is a chopper controller having a multi-valued
duty cycle D, where D = [Di for said chopper controller that produces current Ii (A), 1 < i < n+m]; and
wherein said means for generating currents In+1(A), In+2(A),...,In+m(A) includes function generator means for generating said currents in the armature
windings, said function generator means receiving said command signal A and a signal
representing the duty cycle D.
21. An apparatus as in claim 15 wherein the n spatially fixed windings comprise at
least a separately excited field winding, and wherein the m movable windings comprise
armature windings and wherein said controller is a chopper controller having a multi-valued
duty cycle D, where D =[Di for said chopper controller that produces current Ii (A), 1 < i < n+m]; and
wherein said means for generating currents In+1(A), In+2(A),...,In+m(A) includes function generator means for generating said currents in the armature
windings, said function generator means receiving a signal representing the magnitude
of current in said separately excited field winding and a signal representing the
duty cycle D.